Adderall/Vyvanse/Amphetamines don't interact well at all with vitamin C, of which grapefruits are full of. So sadly enough, you don't get any 5x intake boost with the enjoyable meds. Would have been way too much fun ;)
Maybe someone with journal access can dig out dosage ranges from any of these many sources: https://scholar.google.com/scholar?q=related:4ssWhTcQeYEJ:sc...